Typical displacement ships have good stability to meet the needs for various cargo tonnage. However, when a displacement ship carries more cargo, its hull draft becomes high. An increased draft can cause more water resistance during the ship movement which, in turn, leads to more power consumption and thus makes it difficult to increase its speed and improve its performance.
Hydrofoil crafts can reduce a large portion of water resistance and, therefore, enhance their travel speed. However, Hydrofoil crafts have low load capability and poor seaworthiness.
Surface effect crafts, such as hovercrafts, can reduce water resistance and thus increase their travel speed. However, surface effect crafts are unable to use the hydrodynamic buoyancy to support their weight. Moreover, a large amount of power has been consumed in order for them to generate dynamic air cushion. Further, their advantages can all disappear when there is a raid of lateral wind.
Typical planing boats have low draft in planing state and therefore can have an increased travel speed. They usually adopt a deep or a shallow V-shaped hull to improve the moving stability and lateral stability. However, a planing boat has dihedrals on its hull. Hence, the wet area at the hull bottom and splash at both boards increase to cause more water resistance. Moreover, a planing boat usually rides at an angle relative to the water surface with its bow up high and its stem low, which can further increase water resistance and induce bounce and pitching when traveling at a high speed or on rough waters. Certain improved planing boats, as disclosed in U.S. Pat. Nos. 5,265,554, 5,016,552, 5,231,949, 4,722,294, etc., adopt a shallow V-shaped hull or partly deep-V bottom to acquire certain merits. However, the performance of such improved planing boat are still similar to those V-shaped bottom planing boats. The improvements are very limited.
Sea-knife boats can be one kind of planing boats. They have faster speed and better performance in storms than other planing boats. However, sea-knife boats have triangular plane hull bottoms, which results in reduced stability and poor operative function.